USMLE Question #440: Real Exam Question with Answer & Explanation

A 67-year-old woman who has been in very good health is brought to her physician's office by her husband. He states that over the course of the past 5 years she has had difficulty recognizing her grandchildren, she has not been able to plan their daily activities, she has forgotten things left cooking on the stove, and at night she has been wandering through the house with an absent look on her face. She is beginning to demonstrate difficulty in recalling the names of common objects, and her speech is limited to simple two- or three-word sentences. Which of the following is the most likely diagnosis?